Actor Gregory Peck and novelist Harper Lee on the set of To Kill a Mockingbird in 1962. Photograph: Bettmann/Corbis

Fifty years after it first became a bestseller, Harper Lee's groundbreaking story of racism in the American south, To Kill a Mockingbird, is racing back to the top of the UK's book charts.

Celebrations in libraries, bookshops and cinemas around the country marking the half-century since the novel was first published on 11 July 1960 have sent the modern classic riding high in the bestseller lists once more. This Pulitzer prize-winning debut – the only novel Lee has published so far – sits alongside more modern fare from the likes of Terry Pratchett, Jodi Picoult and Patricia Cornwell in 14th position overall in The Bookseller magazine's official UK top 50.

In the independent bookseller Foyles, To Kill a Mockingbird is currently the number one bestseller following prominent promotions of the 50th anniversary edition. Foyles's web editor Jonathan Ruppin was "delighted that a classic book of such significance, both in terms of its literary impact and the awareness of important issues that it raises, is still being discovered by new generations of readers".

"The elegance and humanity of Harper Lee's writing and the absorbing story she tells mean that it's a book which is unlikely ever to go out of print." While its 1930s setting is increasingly remote, he continued, communities still fighting for equality and justice can still draw inspiration from the novel, "but, above all, it's simply a fantastic read".

Telling the story of lawyer Atticus Finch's defence of a black man charged with the rape of a white girl through the eyes of his children Scout and Jem Finch, the novel takes its title from Finch's advice to his children: "Shoot all the Bluejays you want, if you can hit 'em, but remember it's a sin to kill a Mockingbird."

It has gone on to sell more than 40m copies around the world, and counts Oprah Winfrey, Truman Capote and George W Bush – who awarded Lee the Presidential Medal of Freedom for her "outstanding contribution to America's literary tradition" – among its many fans.

"It is our number seven title, ahead of Barbara Kingsolver, Harlan Coben and Edward Rutherford," said Waterstone's Jon Howells. "It's an amazing achievement for a 50-year-old novel – great to see."

"Booksellers have relished the chance to handsell what is for many their favourite book, and customer response has been exceptional," he added. "I guess it is one of those titles that many people have read, but a long time ago, or have meant to read for a long, long time, and this anniversary is inspiring a lot of people to pick the book up."

The UK's libraries have also been hosting events to discuss and read the book, while cinemas have been holding screenings of the Oscar-winning film adaptation starring Gregory Peck as Atticus Finch, and as well as the 50th anniversary edition of the book, the book's British publisher Arrow has released the UK's first-ever audio version, an unabridged, 11-hour edition read by Sissy Spacek. "She was handpicked by Harper Lee to read it," said spokesperson Ruth Waldram.

Events in the UK pale in comparison to the country-wide festivities in the US, however. From an all-day readathon in North Carolina, a courtroom re-enactment in California and "mocktails and music by the Boo Radleys" in New York, celebrations are centring on Monroeville, Alabama, Lee's hometown and the inspiration for the fictional setting of Maycomb in the novel. A four-day celebration is currently under way, complete with a marathon reading from the book, a walking tour of the town, a feast of the traditional Southern foods described in the novel, and a birthday party on the lawn of the courthouse that features in the book, where the "signature" cocktail, Tequila Mockingbird, will be on offer.

Thousands of fans visit the town every year to pay homage to the novel, and Monroeville is expecting a further influx this weekend. There is still hope that the reclusive 84-year-old Lee, who retired from public life in 1964 following the unexpected success of her only novel, will make an appearance at events, although reports last month suggested that despite receiving an invitation to the celebrations, she will be remaining in her apartment. Her publisher describes her chief interests – apart from writing – as "19th-century literature and 18th-century music, watching politicians and cats, travelling and being alone".

Fifty years after Harper Lee's world-famous Pulitzer prize-winning novel, To Kill a Mockingbird, was first published, we gather together photographs of Lee as her debut novel first found celebrity, the town where the book was set, and the film that was made of it